It is known in the prior art that the frequency of light waves can be captured in silver halide photographic emulsion in the form of vertically embedded standing waves, with a waves nodal points physically representing the frequency. In 1908 Gabriel Lippmann won the Nobel Prize in Physics “for his method of reproducing colours photographically based on the phenomenon of interference” (quoted on the Noble Prize website at nobelprize.org/nobel_prizes/physics/laureates/1908/). This technique was first described in 1891 to store and extract color information from specially constructed black and white photographic plates (Lippmann, G, “La Photographie des Couleurs,” Compte Rendes a l'Academie des Sciences, Tome 112, pp 247-275, February 1891). While never commercialized successfully because of the difficulties of viewing the color image, reproducing the image beyond its first iteration on a glass plate, and the rudimentary, extremely slow photographic chemistry at the time, the Lippmann process is applied in the present invention in a novel methodology and apparatus for the storage of digital data as well as human-readable images and text, as described herein.
The ability to store data using light is generally limited by the wavelength of light. This has recently been exemplified by the introduction of so-called “Blu-Ray” DVD recorders. The shorter wavelength of the blue light source nearly doubles the recording density and, thus, the playing time. However, the lifetimes of such media are relatively short, ranging from a few years to possibly a century or a bit more if extreme care is taken to preserve the media against environmental damage.
In contrast, this invention teaches a methodology and an optical apparatus that provides long-term, archival storage due to the use of a chemically fixed photosensitive emulsion, such as silver halide, for the recording and playback media. In accelerated testing as known in the art, silver- or metallic-based photographic media have been estimated to last upwards of tens of thousands of years, without requiring special energy-intensive storage conditions—a true archival system for future generations (Wilhelm, H, “Long-Term Preservation of Photographic Originals and Digital Image Files . . . ”, IS&T's Archiving 2008 Conference in Bern, Switzerland, Jun. 26, 2008, Society for Imaging Science and Technology, p. 4). In addition, this invention substantially increases optical storage density beyond that of current optical techniques.
The Lippmann process works as follows: The lightwave color palatte contains the information in the form of a ray representing the specific colors. This forward ray (entering through the transparent side of the storage medium) traverses the emulsion and is reflected back from a reflecting layer, (in Lippmann's specific case the reflective layer was a pool of liquid mercury). As the reflected light ray returns through the emulsion it combines with the forward ray, causing interference. This interference results in cancellation of the light at opposing wave nodes and reinforcement at the in-phase nodes. Thus, vertically through the emulsion, there are regularly spaced areas of exposure (where the waves reinforce), followed by areas of zero exposure where the waves cancel. (Mannheim, L A, Photography Theory and Practice, Amphoto, 1970, Vol I, Sect 58; Lippmann, op. cit.)
The Lippmann silver grains as exposed (and developed) are laid down in successive laminae coinciding with the anti-nodal planes of the standing waves recorded, equal to the half-wavelength of the light that forms the waves (Wood, R W, Physical Optics, Macmillan, 1934, pp 214-217, especially FIGS. 137-138 for the laminae). This is known in the art as a “Lippmann emulsion”—a relatively thick, transparent, and extremely fine-grained panchromatic photosensitive coating, as described in Lippmann's interference process. The spacing of the exposed vertical grains literally represents the wavelengths of the specific impinging light. For each color this spacing is, of course, different. A higher frequency (e.g., blue) causes more grains vertically to be exposed in a uniform pattern representing the peak amplitudes of the standing wave, and a lower frequency (e.g., red) causes fewer grains to be exposed vertically (viz.: figures at nobelprize.org, op.cit.; Wood, op.cit.; Mannheim, op. cit.; and Lippmann, op. cit.).
In Lippmann's original process, the colors represented a mapping of the actual colors of a scene focused on the special emulsion by a conventional camera apparatus. A full-color image with Lippmann process is reconstructed by shining a white light source at a critical angle through the developed and fixed emulsion toward the viewer, with the vertical interference columns being observed as the true colors of the original by the human visual system. In contrast, the present invention only needs to record a small region for each data pixel, plus monochromatic images, text and microtext, which simplifies the construction of the plate apparatus for the embodiments described herein.
The Lippmann emulsion is developed, as known in the art, using specified photographic chemistry for its ultra-fine grain processing (Wood, op. cit, pp 215-216; Rich, C, “Lippmann Photographic Process Put to Practice”, SPIE v. 2688, Society of Photo-Optical Instrumentation Engineers (1996), pp. 88-95; U.S. Pat. No. 4,202,695; and Bjelkhagen, H I, Silver-Halide Recording Materials for Holography and Their Processing, Springer, 1995, esp. ch. 2.2.2, pp. 37ff on the preparation and developing formulae for Lippmann emulsions). For the present invention, the development process includes sufficient chemistry to dissolve a reflective layer completely if a reflection layer is deposited, depending on the material used to create it, yielding a plate with sufficient transparency so as to allow the interference patterns not to be obscured for readout. (The present invention's photosensitive plate does not include an anti-halation layer as with conventional photographic film since that would obviate the function of the reflective layer. Therefore this invention's development process need not have chemistry to dissolve such an anti-halation layer).